The present invention relates to picture encoding and decoding. In an important example the pictures form part of a video sequence.
It has long been understood that in lossless encoding, use of a transform such as the Direct Cosine Transform (DCT) can be very effective in permitting coarser quantization of higher spatial frequencies that are less perceptible. The DCT (including approximations and variations) has important advantages. It can be applied separable in horizontal and vertical directions; for this and other reasons it is computationally efficient. Mathematically, it is understood that the DCT (or other separable transforms) falls short of optimum coding efficiency. The Karhunen-Loeve transform (KLT) is often referred to as the optimum transform for coding a signal but the complexity is such that its use in most fields of encoding is wholly impractical.
It would be helpful to improve the efficiency of, for example, the DCT in the context of picture encoding or decoding.